1. Field of the Invention
The invention relates generally to the detection of occlusions in the infusion line of a syringe pump. In particular, the invention relates to a programmable syringe pump which utilizes a novel algorithm to determine whether an occlusion exists in the infusion line.
2. Background of the Invention
A syringe pump is a device for pumping fluid from a syringe into a patient. The syringe is placed in the pump and connected to the patient via an infusion line. During the course of infusing medication into a patient, it is possible for an occlusion to arise in the infusion line. Such a condition, if undetected may cause injury to the patient.
An occlusion in the infusion line will cause the force between the pusher of the syringe pump and the syringe plunger to increase due to increased pressure in the syringe. In the prior art, an occlusion in the infusion line has been detected by a pre-loaded spring which collapses when the force between the pusher of the syringe pump and the plunger increases beyond the predetermined force in the spring. This in turn triggers a switch which alerts the user or shuts off the syringe pump.
More sophisticated syringe pumps monitor the force between the pusher and the plunger by means of a force transducer. The amount of force increase in the syringe corresponding to an occlusion requiring remedial action varies from one syringe to another. For this reason, the force is translated into a pressure. This translation takes into account the frictional force in the syringe and the cross-sectional area of the syringe by use of the formula: ##EQU1## where P=the liquid pressure in the syringe
F=the pushing force measured by the transducer PA1 Ff=the frictional force in the syringe PA1 A=the cross sectional area of the syringe
The frictional force in the syringe and the cross sectional area of the syringe are assumed to be constant. However, in reality (1) the frictional force in the syringe is not constant and varies with pressure; and (2) The cross sectional area of the syringe may also vary with pressure. The prior art force to pressure conversion is there not very accurate.